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<pre><span class="sourceLineNo">001</span>/*<a name="line.1"></a>
<span class="sourceLineNo">002</span> * Copyright (C) 2010 The Guava Authors<a name="line.2"></a>
<span class="sourceLineNo">003</span> *<a name="line.3"></a>
<span class="sourceLineNo">004</span> * Licensed under the Apache License, Version 2.0 (the "License");<a name="line.4"></a>
<span class="sourceLineNo">005</span> * you may not use this file except in compliance with the License.<a name="line.5"></a>
<span class="sourceLineNo">006</span> * You may obtain a copy of the License at<a name="line.6"></a>
<span class="sourceLineNo">007</span> *<a name="line.7"></a>
<span class="sourceLineNo">008</span> * http://www.apache.org/licenses/LICENSE-2.0<a name="line.8"></a>
<span class="sourceLineNo">009</span> *<a name="line.9"></a>
<span class="sourceLineNo">010</span> * Unless required by applicable law or agreed to in writing, software<a name="line.10"></a>
<span class="sourceLineNo">011</span> * distributed under the License is distributed on an "AS IS" BASIS,<a name="line.11"></a>
<span class="sourceLineNo">012</span> * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.<a name="line.12"></a>
<span class="sourceLineNo">013</span> * See the License for the specific language governing permissions and<a name="line.13"></a>
<span class="sourceLineNo">014</span> * limitations under the License.<a name="line.14"></a>
<span class="sourceLineNo">015</span> */<a name="line.15"></a>
<span class="sourceLineNo">016</span><a name="line.16"></a>
<span class="sourceLineNo">017</span>package com.google.common.util.concurrent;<a name="line.17"></a>
<span class="sourceLineNo">018</span><a name="line.18"></a>
<span class="sourceLineNo">019</span>import static com.google.common.base.Preconditions.checkNotNull;<a name="line.19"></a>
<span class="sourceLineNo">020</span><a name="line.20"></a>
<span class="sourceLineNo">021</span>import com.google.common.annotations.Beta;<a name="line.21"></a>
<span class="sourceLineNo">022</span>import com.google.common.base.Throwables;<a name="line.22"></a>
<span class="sourceLineNo">023</span>import com.google.common.collect.Lists;<a name="line.23"></a>
<span class="sourceLineNo">024</span><a name="line.24"></a>
<span class="sourceLineNo">025</span>import java.util.ArrayList;<a name="line.25"></a>
<span class="sourceLineNo">026</span>import java.util.concurrent.TimeUnit;<a name="line.26"></a>
<span class="sourceLineNo">027</span>import java.util.concurrent.locks.Condition;<a name="line.27"></a>
<span class="sourceLineNo">028</span>import java.util.concurrent.locks.ReentrantLock;<a name="line.28"></a>
<span class="sourceLineNo">029</span><a name="line.29"></a>
<span class="sourceLineNo">030</span>import javax.annotation.Nullable;<a name="line.30"></a>
<span class="sourceLineNo">031</span>import javax.annotation.concurrent.GuardedBy;<a name="line.31"></a>
<span class="sourceLineNo">032</span><a name="line.32"></a>
<span class="sourceLineNo">033</span>/**<a name="line.33"></a>
<span class="sourceLineNo">034</span> * A synchronization abstraction supporting waiting on arbitrary boolean conditions.<a name="line.34"></a>
<span class="sourceLineNo">035</span> *<a name="line.35"></a>
<span class="sourceLineNo">036</span> * &lt;p&gt;This class is intended as a replacement for {@link ReentrantLock}. Code using {@code Monitor}<a name="line.36"></a>
<span class="sourceLineNo">037</span> * is less error-prone and more readable than code using {@code ReentrantLock}, without significant<a name="line.37"></a>
<span class="sourceLineNo">038</span> * performance loss. {@code Monitor} even has the potential for performance gain by optimizing the<a name="line.38"></a>
<span class="sourceLineNo">039</span> * evaluation and signaling of conditions.  Signaling is entirely<a name="line.39"></a>
<span class="sourceLineNo">040</span> * &lt;a href="http://en.wikipedia.org/wiki/Monitor_(synchronization)#Implicit_signaling"&gt;<a name="line.40"></a>
<span class="sourceLineNo">041</span> * implicit&lt;/a&gt;.<a name="line.41"></a>
<span class="sourceLineNo">042</span> * By eliminating explicit signaling, this class can guarantee that only one thread is awakened<a name="line.42"></a>
<span class="sourceLineNo">043</span> * when a condition becomes true (no "signaling storms" due to use of {@link<a name="line.43"></a>
<span class="sourceLineNo">044</span> * java.util.concurrent.locks.Condition#signalAll Condition.signalAll}) and that no signals are lost<a name="line.44"></a>
<span class="sourceLineNo">045</span> * (no "hangs" due to incorrect use of {@link java.util.concurrent.locks.Condition#signal<a name="line.45"></a>
<span class="sourceLineNo">046</span> * Condition.signal}).<a name="line.46"></a>
<span class="sourceLineNo">047</span> *<a name="line.47"></a>
<span class="sourceLineNo">048</span> * &lt;p&gt;A thread is said to &lt;i&gt;occupy&lt;/i&gt; a monitor if it has &lt;i&gt;entered&lt;/i&gt; the monitor but not yet<a name="line.48"></a>
<span class="sourceLineNo">049</span> * &lt;i&gt;left&lt;/i&gt;. Only one thread may occupy a given monitor at any moment. A monitor is also<a name="line.49"></a>
<span class="sourceLineNo">050</span> * reentrant, so a thread may enter a monitor any number of times, and then must leave the same<a name="line.50"></a>
<span class="sourceLineNo">051</span> * number of times. The &lt;i&gt;enter&lt;/i&gt; and &lt;i&gt;leave&lt;/i&gt; operations have the same synchronization<a name="line.51"></a>
<span class="sourceLineNo">052</span> * semantics as the built-in Java language synchronization primitives.<a name="line.52"></a>
<span class="sourceLineNo">053</span> *<a name="line.53"></a>
<span class="sourceLineNo">054</span> * &lt;p&gt;A call to any of the &lt;i&gt;enter&lt;/i&gt; methods with &lt;b&gt;void&lt;/b&gt; return type should always be<a name="line.54"></a>
<span class="sourceLineNo">055</span> * followed immediately by a &lt;i&gt;try/finally&lt;/i&gt; block to ensure that the current thread leaves the<a name="line.55"></a>
<span class="sourceLineNo">056</span> * monitor cleanly: &lt;pre&gt;   {@code<a name="line.56"></a>
<span class="sourceLineNo">057</span> *<a name="line.57"></a>
<span class="sourceLineNo">058</span> *   monitor.enter();<a name="line.58"></a>
<span class="sourceLineNo">059</span> *   try {<a name="line.59"></a>
<span class="sourceLineNo">060</span> *     // do things while occupying the monitor<a name="line.60"></a>
<span class="sourceLineNo">061</span> *   } finally {<a name="line.61"></a>
<span class="sourceLineNo">062</span> *     monitor.leave();<a name="line.62"></a>
<span class="sourceLineNo">063</span> *   }}&lt;/pre&gt;<a name="line.63"></a>
<span class="sourceLineNo">064</span> *<a name="line.64"></a>
<span class="sourceLineNo">065</span> * A call to any of the &lt;i&gt;enter&lt;/i&gt; methods with &lt;b&gt;boolean&lt;/b&gt; return type should always appear as<a name="line.65"></a>
<span class="sourceLineNo">066</span> * the condition of an &lt;i&gt;if&lt;/i&gt; statement containing a &lt;i&gt;try/finally&lt;/i&gt; block to ensure that the<a name="line.66"></a>
<span class="sourceLineNo">067</span> * current thread leaves the monitor cleanly: &lt;pre&gt;   {@code<a name="line.67"></a>
<span class="sourceLineNo">068</span> *<a name="line.68"></a>
<span class="sourceLineNo">069</span> *   if (monitor.tryEnter()) {<a name="line.69"></a>
<span class="sourceLineNo">070</span> *     try {<a name="line.70"></a>
<span class="sourceLineNo">071</span> *       // do things while occupying the monitor<a name="line.71"></a>
<span class="sourceLineNo">072</span> *     } finally {<a name="line.72"></a>
<span class="sourceLineNo">073</span> *       monitor.leave();<a name="line.73"></a>
<span class="sourceLineNo">074</span> *     }<a name="line.74"></a>
<span class="sourceLineNo">075</span> *   } else {<a name="line.75"></a>
<span class="sourceLineNo">076</span> *     // do other things since the monitor was not available<a name="line.76"></a>
<span class="sourceLineNo">077</span> *   }}&lt;/pre&gt;<a name="line.77"></a>
<span class="sourceLineNo">078</span> *<a name="line.78"></a>
<span class="sourceLineNo">079</span> * &lt;h2&gt;Comparison with {@code synchronized} and {@code ReentrantLock}&lt;/h2&gt;<a name="line.79"></a>
<span class="sourceLineNo">080</span> * <a name="line.80"></a>
<span class="sourceLineNo">081</span> * &lt;p&gt;The following examples show a simple threadsafe holder expressed using {@code synchronized},<a name="line.81"></a>
<span class="sourceLineNo">082</span> * {@link ReentrantLock}, and {@code Monitor}.<a name="line.82"></a>
<span class="sourceLineNo">083</span> * <a name="line.83"></a>
<span class="sourceLineNo">084</span> * &lt;h3&gt;{@code synchronized}&lt;/h3&gt;<a name="line.84"></a>
<span class="sourceLineNo">085</span> * <a name="line.85"></a>
<span class="sourceLineNo">086</span> * &lt;p&gt;This version is the fewest lines of code, largely because the synchronization mechanism used<a name="line.86"></a>
<span class="sourceLineNo">087</span> * is built into the language and runtime. But the programmer has to remember to avoid a couple of<a name="line.87"></a>
<span class="sourceLineNo">088</span> * common bugs: The {@code wait()} must be inside a {@code while} instead of an {@code if}, and<a name="line.88"></a>
<span class="sourceLineNo">089</span> * {@code notifyAll()} must be used instead of {@code notify()} because there are two different<a name="line.89"></a>
<span class="sourceLineNo">090</span> * logical conditions being awaited. &lt;pre&gt;   {@code<a name="line.90"></a>
<span class="sourceLineNo">091</span> *<a name="line.91"></a>
<span class="sourceLineNo">092</span> *   public class SafeBox&lt;V&gt; {<a name="line.92"></a>
<span class="sourceLineNo">093</span> *     private V value;<a name="line.93"></a>
<span class="sourceLineNo">094</span> *<a name="line.94"></a>
<span class="sourceLineNo">095</span> *     public synchronized V get() throws InterruptedException {<a name="line.95"></a>
<span class="sourceLineNo">096</span> *       while (value == null) {<a name="line.96"></a>
<span class="sourceLineNo">097</span> *         wait();<a name="line.97"></a>
<span class="sourceLineNo">098</span> *       }<a name="line.98"></a>
<span class="sourceLineNo">099</span> *       V result = value;<a name="line.99"></a>
<span class="sourceLineNo">100</span> *       value = null;<a name="line.100"></a>
<span class="sourceLineNo">101</span> *       notifyAll();<a name="line.101"></a>
<span class="sourceLineNo">102</span> *       return result;<a name="line.102"></a>
<span class="sourceLineNo">103</span> *     }<a name="line.103"></a>
<span class="sourceLineNo">104</span> *<a name="line.104"></a>
<span class="sourceLineNo">105</span> *     public synchronized void set(V newValue) throws InterruptedException {<a name="line.105"></a>
<span class="sourceLineNo">106</span> *       while (value != null) {<a name="line.106"></a>
<span class="sourceLineNo">107</span> *         wait();<a name="line.107"></a>
<span class="sourceLineNo">108</span> *       }<a name="line.108"></a>
<span class="sourceLineNo">109</span> *       value = newValue;<a name="line.109"></a>
<span class="sourceLineNo">110</span> *       notifyAll();<a name="line.110"></a>
<span class="sourceLineNo">111</span> *     }<a name="line.111"></a>
<span class="sourceLineNo">112</span> *   }}&lt;/pre&gt;<a name="line.112"></a>
<span class="sourceLineNo">113</span> * <a name="line.113"></a>
<span class="sourceLineNo">114</span> * &lt;h3&gt;{@code ReentrantLock}&lt;/h3&gt;<a name="line.114"></a>
<span class="sourceLineNo">115</span> * <a name="line.115"></a>
<span class="sourceLineNo">116</span> * &lt;p&gt;This version is much more verbose than the {@code synchronized} version, and still suffers<a name="line.116"></a>
<span class="sourceLineNo">117</span> * from the need for the programmer to remember to use {@code while} instead of {@code if}.<a name="line.117"></a>
<span class="sourceLineNo">118</span> * However, one advantage is that we can introduce two separate {@code Condition} objects, which<a name="line.118"></a>
<span class="sourceLineNo">119</span> * allows us to use {@code signal()} instead of {@code signalAll()}, which may be a performance<a name="line.119"></a>
<span class="sourceLineNo">120</span> * benefit. &lt;pre&gt;   {@code<a name="line.120"></a>
<span class="sourceLineNo">121</span> *<a name="line.121"></a>
<span class="sourceLineNo">122</span> *   public class SafeBox&lt;V&gt; {<a name="line.122"></a>
<span class="sourceLineNo">123</span> *     private final ReentrantLock lock = new ReentrantLock();<a name="line.123"></a>
<span class="sourceLineNo">124</span> *     private final Condition valuePresent = lock.newCondition();<a name="line.124"></a>
<span class="sourceLineNo">125</span> *     private final Condition valueAbsent = lock.newCondition();<a name="line.125"></a>
<span class="sourceLineNo">126</span> *     private V value;<a name="line.126"></a>
<span class="sourceLineNo">127</span> *<a name="line.127"></a>
<span class="sourceLineNo">128</span> *     public V get() throws InterruptedException {<a name="line.128"></a>
<span class="sourceLineNo">129</span> *       lock.lock();<a name="line.129"></a>
<span class="sourceLineNo">130</span> *       try {<a name="line.130"></a>
<span class="sourceLineNo">131</span> *         while (value == null) {<a name="line.131"></a>
<span class="sourceLineNo">132</span> *           valuePresent.await();<a name="line.132"></a>
<span class="sourceLineNo">133</span> *         }<a name="line.133"></a>
<span class="sourceLineNo">134</span> *         V result = value;<a name="line.134"></a>
<span class="sourceLineNo">135</span> *         value = null;<a name="line.135"></a>
<span class="sourceLineNo">136</span> *         valueAbsent.signal();<a name="line.136"></a>
<span class="sourceLineNo">137</span> *         return result;<a name="line.137"></a>
<span class="sourceLineNo">138</span> *       } finally {<a name="line.138"></a>
<span class="sourceLineNo">139</span> *         lock.unlock();<a name="line.139"></a>
<span class="sourceLineNo">140</span> *       }<a name="line.140"></a>
<span class="sourceLineNo">141</span> *     }<a name="line.141"></a>
<span class="sourceLineNo">142</span> *<a name="line.142"></a>
<span class="sourceLineNo">143</span> *     public void set(V newValue) throws InterruptedException {<a name="line.143"></a>
<span class="sourceLineNo">144</span> *       lock.lock();<a name="line.144"></a>
<span class="sourceLineNo">145</span> *       try {<a name="line.145"></a>
<span class="sourceLineNo">146</span> *         while (value != null) {<a name="line.146"></a>
<span class="sourceLineNo">147</span> *           valueAbsent.await();<a name="line.147"></a>
<span class="sourceLineNo">148</span> *         }<a name="line.148"></a>
<span class="sourceLineNo">149</span> *         value = newValue;<a name="line.149"></a>
<span class="sourceLineNo">150</span> *         valuePresent.signal();<a name="line.150"></a>
<span class="sourceLineNo">151</span> *       } finally {<a name="line.151"></a>
<span class="sourceLineNo">152</span> *         lock.unlock();<a name="line.152"></a>
<span class="sourceLineNo">153</span> *       }<a name="line.153"></a>
<span class="sourceLineNo">154</span> *     }<a name="line.154"></a>
<span class="sourceLineNo">155</span> *   }}&lt;/pre&gt;<a name="line.155"></a>
<span class="sourceLineNo">156</span> * <a name="line.156"></a>
<span class="sourceLineNo">157</span> * &lt;h3&gt;{@code Monitor}&lt;/h3&gt;<a name="line.157"></a>
<span class="sourceLineNo">158</span> * <a name="line.158"></a>
<span class="sourceLineNo">159</span> * &lt;p&gt;This version adds some verbosity around the {@code Guard} objects, but removes that same<a name="line.159"></a>
<span class="sourceLineNo">160</span> * verbosity, and more, from the {@code get} and {@code set} methods. {@code Monitor} implements the<a name="line.160"></a>
<span class="sourceLineNo">161</span> * same efficient signaling as we had to hand-code in the {@code ReentrantLock} version above.<a name="line.161"></a>
<span class="sourceLineNo">162</span> * Finally, the programmer no longer has to hand-code the wait loop, and therefore doesn't have to<a name="line.162"></a>
<span class="sourceLineNo">163</span> * remember to use {@code while} instead of {@code if}. &lt;pre&gt;   {@code<a name="line.163"></a>
<span class="sourceLineNo">164</span> *<a name="line.164"></a>
<span class="sourceLineNo">165</span> *   public class SafeBox&lt;V&gt; {<a name="line.165"></a>
<span class="sourceLineNo">166</span> *     private final Monitor monitor = new Monitor();<a name="line.166"></a>
<span class="sourceLineNo">167</span> *     private final Monitor.Guard valuePresent = new Monitor.Guard(monitor) {<a name="line.167"></a>
<span class="sourceLineNo">168</span> *       public boolean isSatisfied() {<a name="line.168"></a>
<span class="sourceLineNo">169</span> *         return value != null;<a name="line.169"></a>
<span class="sourceLineNo">170</span> *       }<a name="line.170"></a>
<span class="sourceLineNo">171</span> *     };<a name="line.171"></a>
<span class="sourceLineNo">172</span> *     private final Monitor.Guard valueAbsent = new Monitor.Guard(monitor) {<a name="line.172"></a>
<span class="sourceLineNo">173</span> *       public boolean isSatisfied() {<a name="line.173"></a>
<span class="sourceLineNo">174</span> *         return value == null;<a name="line.174"></a>
<span class="sourceLineNo">175</span> *       }<a name="line.175"></a>
<span class="sourceLineNo">176</span> *     };<a name="line.176"></a>
<span class="sourceLineNo">177</span> *     private V value;<a name="line.177"></a>
<span class="sourceLineNo">178</span> *<a name="line.178"></a>
<span class="sourceLineNo">179</span> *     public V get() throws InterruptedException {<a name="line.179"></a>
<span class="sourceLineNo">180</span> *       monitor.enterWhen(valuePresent);<a name="line.180"></a>
<span class="sourceLineNo">181</span> *       try {<a name="line.181"></a>
<span class="sourceLineNo">182</span> *         V result = value;<a name="line.182"></a>
<span class="sourceLineNo">183</span> *         value = null;<a name="line.183"></a>
<span class="sourceLineNo">184</span> *         return result;<a name="line.184"></a>
<span class="sourceLineNo">185</span> *       } finally {<a name="line.185"></a>
<span class="sourceLineNo">186</span> *         monitor.leave();<a name="line.186"></a>
<span class="sourceLineNo">187</span> *       }<a name="line.187"></a>
<span class="sourceLineNo">188</span> *     }<a name="line.188"></a>
<span class="sourceLineNo">189</span> *<a name="line.189"></a>
<span class="sourceLineNo">190</span> *     public void set(V newValue) throws InterruptedException {<a name="line.190"></a>
<span class="sourceLineNo">191</span> *       monitor.enterWhen(valueAbsent);<a name="line.191"></a>
<span class="sourceLineNo">192</span> *       try {<a name="line.192"></a>
<span class="sourceLineNo">193</span> *         value = newValue;<a name="line.193"></a>
<span class="sourceLineNo">194</span> *       } finally {<a name="line.194"></a>
<span class="sourceLineNo">195</span> *         monitor.leave();<a name="line.195"></a>
<span class="sourceLineNo">196</span> *       }<a name="line.196"></a>
<span class="sourceLineNo">197</span> *     }<a name="line.197"></a>
<span class="sourceLineNo">198</span> *   }}&lt;/pre&gt;<a name="line.198"></a>
<span class="sourceLineNo">199</span> * <a name="line.199"></a>
<span class="sourceLineNo">200</span> * @author Justin T. Sampson<a name="line.200"></a>
<span class="sourceLineNo">201</span> * @since 10.0<a name="line.201"></a>
<span class="sourceLineNo">202</span> */<a name="line.202"></a>
<span class="sourceLineNo">203</span>@Beta<a name="line.203"></a>
<span class="sourceLineNo">204</span>public final class Monitor {<a name="line.204"></a>
<span class="sourceLineNo">205</span>  // TODO: Use raw LockSupport or AbstractQueuedSynchronizer instead of ReentrantLock.<a name="line.205"></a>
<span class="sourceLineNo">206</span><a name="line.206"></a>
<span class="sourceLineNo">207</span>  /**<a name="line.207"></a>
<span class="sourceLineNo">208</span>   * A boolean condition for which a thread may wait. A {@code Guard} is associated with a single<a name="line.208"></a>
<span class="sourceLineNo">209</span>   * {@code Monitor}. The monitor may check the guard at arbitrary times from any thread occupying<a name="line.209"></a>
<span class="sourceLineNo">210</span>   * the monitor, so code should not be written to rely on how often a guard might or might not be<a name="line.210"></a>
<span class="sourceLineNo">211</span>   * checked.<a name="line.211"></a>
<span class="sourceLineNo">212</span>   * <a name="line.212"></a>
<span class="sourceLineNo">213</span>   * &lt;p&gt;If a {@code Guard} is passed into any method of a {@code Monitor} other than the one it is<a name="line.213"></a>
<span class="sourceLineNo">214</span>   * associated with, an {@link IllegalMonitorStateException} is thrown.<a name="line.214"></a>
<span class="sourceLineNo">215</span>   *<a name="line.215"></a>
<span class="sourceLineNo">216</span>   * @since 10.0<a name="line.216"></a>
<span class="sourceLineNo">217</span>   */<a name="line.217"></a>
<span class="sourceLineNo">218</span>  @Beta<a name="line.218"></a>
<span class="sourceLineNo">219</span>  public abstract static class Guard {<a name="line.219"></a>
<span class="sourceLineNo">220</span>    <a name="line.220"></a>
<span class="sourceLineNo">221</span>    final Monitor monitor;<a name="line.221"></a>
<span class="sourceLineNo">222</span>    final Condition condition;<a name="line.222"></a>
<span class="sourceLineNo">223</span><a name="line.223"></a>
<span class="sourceLineNo">224</span>    @GuardedBy("monitor.lock")<a name="line.224"></a>
<span class="sourceLineNo">225</span>    int waiterCount = 0;<a name="line.225"></a>
<span class="sourceLineNo">226</span><a name="line.226"></a>
<span class="sourceLineNo">227</span>    protected Guard(Monitor monitor) {<a name="line.227"></a>
<span class="sourceLineNo">228</span>      this.monitor = checkNotNull(monitor, "monitor");<a name="line.228"></a>
<span class="sourceLineNo">229</span>      this.condition = monitor.lock.newCondition();<a name="line.229"></a>
<span class="sourceLineNo">230</span>    }<a name="line.230"></a>
<span class="sourceLineNo">231</span><a name="line.231"></a>
<span class="sourceLineNo">232</span>    /**<a name="line.232"></a>
<span class="sourceLineNo">233</span>     * Evaluates this guard's boolean condition. This method is always called with the associated<a name="line.233"></a>
<span class="sourceLineNo">234</span>     * monitor already occupied. Implementations of this method must depend only on state protected<a name="line.234"></a>
<span class="sourceLineNo">235</span>     * by the associated monitor, and must not modify that state.<a name="line.235"></a>
<span class="sourceLineNo">236</span>     */<a name="line.236"></a>
<span class="sourceLineNo">237</span>    public abstract boolean isSatisfied();<a name="line.237"></a>
<span class="sourceLineNo">238</span><a name="line.238"></a>
<span class="sourceLineNo">239</span>    @Override<a name="line.239"></a>
<span class="sourceLineNo">240</span>    public final boolean equals(Object other) {<a name="line.240"></a>
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<span class="sourceLineNo">689</span>   * monitoring of the system state, not for synchronization control.<a name="line.689"></a>
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<span class="sourceLineNo">696</span>   * Returns whether the current thread is occupying this monitor (has entered more times than it<a name="line.696"></a>
<span class="sourceLineNo">697</span>   * has left).<a name="line.697"></a>
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<span class="sourceLineNo">942</span>}<a name="line.942"></a>




























































</pre>
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